Refrigerants are used throughout the world in machines to provide temperature control in the industrial areas of food processing, storage, and distribution in mechanical air conditioning for homes, buildings and automobiles, and in the chemical industry. Since 1860, with the development of the basic concepts of today's refrigeration system, refrigerants for vapor-compression systems were sought which were stable, incombustible, nontoxic and nonirritating chemical fluids which vaporize and condense at pressures and temperatures appropriate for their application. In about 1930, it was discovered that certain halogenated hydrocarbons having chlorine and fluorine atoms could be employed as "safe" refrigerants. These halogenated hydrocarbons include chlorofluorocarbons (CFC's) and hydrochlorofluorocarbons (HCFC's). Recently, it was discovered that some of these "safe" refrigerants are harmful to the environment, and in particular, the release of CFC's to the atmosphere could lead to damaging of the earth's ozone layer. In the atmosphere they can migrate to the stratosphere where photolysis reactions release the chlorine atoms, which can react with ozone. As a result many Western countries have regulations for the elimination of production of CFC's by Jan. 1, 1996. HCFC's have a hydrogen atom in the molecule which can reduce the stability of the compound relative to CFC's. HCFC's are now considered part of the ozone depletion problem and their production is to be phased out (eliminated) by the year 2030. Hydrofluorocarbons (HFC's) are the replacements for CFC's and HCFC's. Examples of CFC's, HCFC's, and HFC's are given in Table 2 of the 1993 ASHRAE FUNDAMENTALS HANDBOOK, American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc., Atlanta, Ga. page 16.4, which is herein incorporated by reference. Because CFC's and HCFC's may be found in the refrigeration systems of old refrigerators, automobiles, and commercial refrigeration facilities, it is desired to have a "safe", simple and economical way of recovering and/or purifying these compounds with a minimum risk of their release to the environment.
Typically, during the continued operation of a refrigeration system, the refrigerant becomes contaminated with impurities such as water vapor, air, acids and particulate matter. In the past, when a refrigeration system needed repair, the standard practice was to vent or bleed the refrigerant to the atmosphere. This technique wasted refrigerant, which can be cleaned and reused, and added a material to the atmosphere, which is now known to cause damage to the ozone layer.
Various methods have been employed to recover and purify refrigerant from refrigeration units. Some of these methods remove the contaminated refrigerant from the refrigeration units, expand the contaminated refrigerant and remove the impurities by condensation. U.S. Pat. No. 4,939,903 to Goddard is an example of this impurity condensation approach. In these systems, it is critical to maintain the system under pressure at all times to prevent any leakage of the refrigerant to the atmosphere.
Others have developed devices for receiving and dispensing a gaseous refrigerant. For example, U.S. Pat. No. 5,165,247 discloses such a device comprising a pressurized vessel, containing an adsorbent, wherein the adsorbent is secured to a heat exchange surface. The pressurized vessel is connected to refrigeration systems to collect or refill the refrigeration system using either cooling to adsorb refrigerant during a collection operation, or heating to desorb refrigerant during a refill operation.
The U.S. Pat. No. 5,094,087 discloses an apparatus incorporating a purifying filter for reclaiming and recovering volatile liquids such as a refrigerant contained in a closed network. The purifying filter includes an oil mist filter and a moisture adsorbing filter, and the filters are arranged in a flow connection between a discharge side of the compressor and the condenser in a refrigeration system. The filters are periodically removed from the closed net work by switch valve means for air drying.
European Patent No. EPO317709B1 discloses a process for disposing of refrigerant from sealed refrigeration systems by opening the system allowing the refrigerant to depressurize and flow to a collecting vessel containing an activated carbon adsorbent. The activated carbon adsorbent adsorbs the refrigerant and permits any air in the system to pass through the collecting vessel, or a group of such vessels connected in series to one another.
In another similar device, U.S. Pat. No. 5,245,839 discloses an apparatus which employs an adsorbent to adsorb refrigerant in a vessel. The adsorbed refrigerant is desorbed with heat to provide a refrigerant gas which is subsequently condensed to a liquid, dried to remove water from the liquid and purged to remove non-condensable gas before returning the refrigerant liquid to a refrigerant reservoir.
U.S. Pat. No. 5,231,980 to Filipovic et at. discloses a process for the recovery of halogenated hydrocarbons from a gas stream, such as anaesthesia in patient exhalent, by passing the gas through a hydrophobic high silica zeolite molecular sieve having a silica to alumina ratio (SiO.sub.2 /Al.sub.2 O.sub.3) of about 12 or greater. The process passes the gas stream through the adsorbent material until just prior to breakthrough. The adsorbed halogenated hydrocarbons are removed from the adsorbent by purging the adsorbent with an inert gas stream at desorption conditions. The halogenated hydrocarbons are subsequently removed from the purging gas stream by condensation, and the condensate is purified by fractional distillation for reuse. The preferred high silica zeolite adsorbent is silicalite.
All of these devices employ separate purification steps requiring additional equipment and liquid or gas handling steps which complicate the process of recovering and purification of refrigerants and increase the risk of escape of refrigerant to the atmosphere. Processes are sought which combine the steps of collecting and purification without requiring additional separation, filtering and purging steps.
Methods are sought which provide for low energy collection and recovery of the refrigerant with a minimum risk of loss of any refrigerant to the environment and with a minimum use of energy in that recovery.